Embodiments of the disclosed technology refer to an electrowetting display (EWD) unit and an electrowetting display device.
The electrowetting display technology is a type of display technology that was introduced in recent years. The electrowetting display technology has the advantages such as bistable displaying, excellent reflectivity, low consumption, wide temperature range, and rapid response, and therefore has drawn increasing attention. Although the electrowetting display technology is now developed in its initial stage, but it may become an important display technology in the future due to its good characteristics and the potential for future development.
The electrowetting display technology is such a technology which controls the interface between fluids that is surrounded (or confined) by sidewalls, by applying a voltage, to cause a change of an electrowetting display unit (typically one pixel unit within a display device). FIG. 1a is a schematic cross-sectional view illustrating a conventional electrowetting display unit in a dark state when no voltage is applied. The conventional electrowetting display unit 100 shown in FIG. 1a includes a fluid chamber 10, a medium layer 3, and an electrode 4. The fluid chamber 10 is defined by side walls (not shown), a polar fluid 1 is provided in the upper portion of the fluid chamber 10, and a non-polar fluid 2 is provided in the lower portion of the fluid chamber 10. In the dark state, the non-polar fluid 2 at the lower portion of the fluid chamber is between the polar fluid 1 and the medium layer 3. During operation of the electrowetting display, the layer of the non-polar fluid 2 can have two functions. One of the functions is a blocking function generally used in a black-white mode display, in which the non-polar fluid layer blocks light or colors and typically is in the black color for a user. The other function is a displaying function generally used in a color mode display, in which the non-polar fluid layer is colored. As shown in FIG. 1a, when no voltage is applied, the non-polar fluid 2 is formed in a flat thin film on the medium layer 3, so that one colored pixel point can observed. When a voltage is applied between the electrode 4 and the polar fluid 1 to realize a bright state for displaying, the contact surfaces of the polar fluid 1 and the medium layer 3 are polarized to have an increased surface energy, thus the surface tensile in the contact surfaces are changed. What is resulted is that the medium layer 3 becomes not hydrophobic any more, and the original stationary state of the display unit becomes not stable any more, so the non-polar fluid 2 is moved to a corner of the display unit so as to form one partially transparent pixel point. FIG. 1b is a cross-sectional view of the conventional electrowetting display unit in a bright state.
When different pixels of the display device are individually driven to display images, the non-polar fluids in the pixels are colored to present different kinds of colors and so as to perform colorful displaying. In theory, any color can be accorded to the display pixels so as to obtain desirable display results. When an electrowetting display unit is employed in a black-white mode display, the non-polar fluid is in the black color. FIGS. 2a and 2b are cross-sectional views illustrating a part of electrowetting display device comprising three electrowetting display units 100 (i.e., three pixels) in a dark state and a bright state, respectively. Separation walls 20 for separating two adjacent display units 100 (i.e., two adjacent pixels) are provided as shown in FIGS. 2a and 2b and are also used to surround (confine) the polar fluid 1 and the non-polar fluid 2 in each display unit.
FIGS. 3a and 3b show top views of the display results from the electrowetting display device including a plurality of display units 100 (e.g., a pixel array) in the dark state when a driving voltage is not applied and in the bright state when a driving voltage is applied, respectively. As shown in FIG. 3b, most part of the pixel array of the electrowetting display device shows the bright state for the outside, but one corner in each pixel unit 100 is still in the dark state for the outside.
As described above, although the electrowetting display technology has many advantages, but when a driving voltage is applied between the polar fluid and the non-polar fluid in each pixel unit for displaying in a bright state, as represented by the arrows in FIGS. 1b, 2b, and 3b, the non-polar fluid shrinks but still remains at one corner of the pixel unit, thus a complete uniform displaying cannot be obtained in the bright state. Especially, when the electrowetting display is used in a black-white mode display, a full-white display cannot be realized and the black non-polar fluid can still be observed at the corner of each pixel unit. The visibility of the colored non-polar fluid in pixel units reduces the contrast and transmittance of the display device, so that a good display quality cannot be ensured. That is, in the bright state, the non-polar fluid also occupies some areas of the pixel unit which lowers the display quality.